The present invention relates to an avalanche photodiode for use in a device for converting a light signal into an electric signal, and more particularly to an avalanche photodiode with a considerably reduced avalanche breakdown voltage, without reducing other performance characteristics.
Detection of a light signal by the use of a rectification barrier or a p-n junction which is biased in the reverse direction has been well known in the art, and a semiconductor device for this purpose is called an avalanche photodiode (hereinafter represented as APD for simplicity). Since an APD utilizes the avalanche phenomenon and hence it has a self-amplification function, it is suitable for use in a detecting device for a light signal. Accordingly, the APD is considered most suitable as a light detecting device in optical communication systems.
In an optical communication system which utilizes semiconductor lasers and APDs, a low operation voltage is an important feature and an advantage. If a high voltage source is necessary to drive the APDs, the feature or advantage of the system will be lost. Further, electrical supply of high voltages to repeaters in order to drive APDs will bring about difficult problems in designing the system. From these reasons, it is desirable that the operation voltage for APDs be nearly the same as the driving voltage for integrated circuits, or otherwise be about 200 volts or less in considering the operating voltages and of electronic parts other than APDs.